1. Field
Embodiments of the present invention relate to a method for manufacturing a device, a lithographic apparatus, a design for manufacturing system, a computer program product for use with a lithographic apparatus and a computer program product for use with a design for manufacturing system.
2. Background
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of devices such as integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
U.S. Pat. Appl. Publ. No. 2005/028129 A1, incorporated herein by reference in its entirety, describes a method to automatically determine beam condition parameters from a target layout. In particular, to determine a numerical aperture (NA) of the radiation beam and an intensity distribution of the radiation in a pupil of the optical system of the lithographic apparatus, such as the sigma_inner and sigma_outer of an annular pupil filling. U.S. Pat. Appl. Publ. No. 2005/028129 A1 uses e.g. a line width analysis or pitch analysis to determine NA and sigma_inner and sigma_outer such that the features may be printed without bias adjustments.
Although the method described in U.S. Pat. Appl. Publ. No. 2005/028129 A1 provides an improvement over earlier prior art methods by effectively adjusting the optical system so as to achieve an imaging with an optimal resolution, the method may still give rise to some problems. For example, when a large NA is selected with a large pupil filling, the depth of focus of the imaging is very small and the risk of not being in optimal focus may be significant. When the imaging is done without having optimal focus, the imaging resolution may be of a lesser quality and the highest resolution features may be imaged with a too low quality.